New gasoline and gas barrier from plasticized carbon black reinforced butyl rubber/high‐density polyethylene blends

The effects of the high‐density polyethylene volume fraction on the curing characteristics and network structure of rubber blends have been studied in terms of the torque, scorch time, optimum curing time, Mooney viscosity, number of elastically effective chains, viscosity, interfacial tension, glass‐transition temperature, scanning electron microscopy, internal friction, sound velocity, acoustic attenuation, polymer–solvent interaction parameter, swelling index, and gel fraction. The applicability of the blends for gasoline barriers has been examined through the changes in the electrical resistance and volumetric swelling in gasoline versus time at room temperature. The transport mechanism of the solvent through the crosslinked butyl rubber/high‐density polyethylene blends is governed by Fickian diffusion law. The transport coefficients, namely, the diffusion coefficient, intrinsic diffusion, and permeation coefficient, have been computed. The experimental data for the permeation coefficient are in good agreement with the values calculated by Maxwell's model and far from those of Robeson's model. In addition, some thermodynamics parameters, namely, the standard entropy, standard enthalpy, and standard Gibbs free energy, have been estimated as functions of the high‐density polyethylene concentration of the butyl rubber blends. Furthermore, the applicability of butyl rubber/high‐density polyethylene composites for Freon gas barriers and antistatic charge dissipation has been examined. Finally, the mechanical properties, such as the tensile strength, hardness, stiffness, and elongation at break, of butyl rubber composites with different high‐density polyethylene concentrations have been evaluated. The increase in the mechanical properties is due to the increase in the crosslinking density and the interfacial adhesion of the blend. This proves that these new blends have important technological applications as gasoline and Freon barriers and for antistatic charge dissipation with good mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1237–1247, 2006     

Dielectric relaxation of poly(tetrafluoroethylene–perfluorovinyl ether) films

Dielectric constant and dielectric loss have been studied for poly(tetrafluoroethylene–perfluorovinyl ether) (PFA) films over a wide temperature range in the frequency range 0.1–100 kHz. Two relaxation peaks were observed, one at room temperature (α_a-relaxation) and the other in the range 170–140 K (β-relaxation), with activation energies of 143·2 and 16·4 kcal/mol, respectively. The β-absorption is attributed to the short segmental local mode motion of the main chains. The α_a-relaxation can be interpreted as due to large-scale conformational rearrangement. The Cole–Cole diagrams are given at different temperatures and the distribution parameters (ϵ₀–ϵ_∞) and (1–α) of the relaxation times were calculated. The X-ray diffraction pattern of PFA shows both a diffuse halo and sharp reflections, characteristic of amorphous and crystalline phases of conventional semicrystalline polymers. Also, no evidence of crystallinity in the films due to thermal treatment during dielectric measurements was observed. IR spectra revealed the absence of any new peaks after the heat treatment.     

Tensile properties and fracture characteristics of ECAP-processed Al and Al-Cu alloys

In the present paper, billets of pure Al, and cast-homogenized Al-2 wt.%, 3 wt.%, and 5 wt.% Cu alloys were successfully processed by equal channel angular pressing (ECAP) up to 10 passes without fracture at room temperature using a die with a channel angle of 110°. Giant strains imposed on workpieces lead to extreme dislocation densities, microstructural refinement, and finally ultrafine grained materials. Tensile tests were employed to examine the fracture modes and fracture surface morphologies of the ECAP-processed Al and Al-Cu alloy samples. In particular, the effects of the number of ECAP passes and the Cu content were investigated.     

Ab initio characterization of Ti decorated SWCNT for hydrogen storage

Characterization has been performed on basis of several physicochemical parameters. The results indicate that the preferential adsorption is on Ti atom deposited on the top site of the (5,5) armchair SWCNT with energies (−0.44 and −0.71) eV for H₂ oriented parallel to the (x) and (y) axes respectively. The binding of H₂ is mostly dominated by the support-metal E (i)^S?Ti term. The role of the SWCNT is not restricted to support the metal. Significant reduction of the energy gap is observed when H₂ are anchored on the external surface of the SWCNT. The SWCNT?Ti?H₂(x) complex is the least reactive configuration with nucleophiles. The calculated parameters characterize H₂ that is oriented parallel to the (x)-[100] axis of the SWCNT to be the most suitable configuration for hydrogen storage based on the recommended adsorption energy range of DOE (−0.2 to −0.6) eV.     

Electrodeposition of CoMoP thin film as diffusion barrier layer for ULSI applications

CoMoP thin films were fabricated by electrodeposition technique from citrate based bath onto Cu sheets for the application as diffusion barriers and metal capping layers in the copper interconnect technology. The study focused on the effect of (NH₄)₆Mo₇O₂₄·4H₂O concentrations in the plating solution on the plating rate and chemical composition of the deposited layer. It was found that the Mo wt.% in the deposited layer increased from 13 to 22 wt.% with increasing (NH₄)₆Mo₇O₂₄·4H₂O concentration. The influence of deposition current density, solution pH and deposition temperature at certain (NH₄)₆Mo₇O₂₄·4H₂O concentration in the plating bath on the plating rate and chemical composition was studied. Polarization behavior of induced co-deposition of CoMoP at various electrolyte pH values was studied using cyclic voltammetry and chronoamperometry to estimate the current efficiency (CE%) of the plating solutions and the optimum pH for the plating process. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques have been applied to characterize the morphology and chemical composition of the deposited layer. CoMoP alloys of high P wt.% as-deposited films showed irregular microcracks amorphous structure and of low P wt.% showed amorphous/nanocrystalline structure while, after annealing at 400 °C for 1 h, the films deposited with low and high P wt.% converted into polycrystalline structure. The results of oxidation property showed that, the Co-13.2 wt.% Mo-10.3 wt.% P alloy has highest stability against oxidation and lowest electrical resistance values (100-150 µΩ). The ferromagnetism nature of coated materials has been studied by hysteresis loop measurements. The electrochemical corrosion results were calculated from polarization studies for as-plated and annealed CoMoP coatings in 3.5% NaCl solution.     

A novel facile synthesis and electromagnetic wave shielding effectiveness at microwave frequency of graphene oxide paper

Nano-structured graphene oxide (GO) freestanding paper was synthesized by an arc recharge technique in flowing of oxygen for the first time. This technique offers new ways on how e.g. layers structure nanomaterials could be produced. The morphology and structural properties of the as-synthesized GO were examined by means of X-ray diffraction, Fourier transform infrared spectra, scanning electrom microscopy, energy dispersive x-ray spectroscopy, transmission electron microscopy, high resolution transmission electron microscopy and selective area electron diffraction techniques. The structural and morphological characterizations revealed that the synthesized GO were well-defined nanosheets with a thickness of 6 nm. The optical band gap was calculated from the absorption spectrum, and was found to be 3.32 eV. Furthermore, we aim to use GO paper to develop new electromagnetic interference shielding sheets that have a high shielding effectiveness (SE) (over 30 dB) at frequencies in the 1–12 GHz range. The complex permittivity and total shielding effectiveness of as synthesized GO freestanding paper are measured at frequencies from 1 to 12 GHz. Finally, to enhance the performances of the electromagnetic shields effectiveness, five-layered GO sheets were made. Furthermore, the highest SE for the light-weight freestanding GO paper was 50 dB at 1 GHz, indicating commercial use for many industrial or military shielding applications as an attractive candidate for the new type of microwave shielding.     

Electrochemical Formation of a Failure Preventing Film on Nickel Surface in Borate Solutions

Cyclic voltammograms (CVs) of the Ni electrode are traced in Na₂B₄O₇ solutions as a function of electrolyte concentration, voltage scanning range, and rate in order to determine the nature of failure protective species formed in the slightly alkaline media. The species formed on the Ni electrode are found to depend on the sweep number due to changes in the activation state of the electrode surface. The voltammograms are characterized by a pronounced anodic peak due to the formation of NiO and a protective passive film corresponding to the formation of β-Ni(OH)₂ before the evolution of oxygen. An additional anodic peak in the vicinity of oxygen evolution potential appeared in the advanced cycles that is attributed to the transformation of β-Ni(OH)₂ to β-NiOOH. The cathodic branch shows only one peak corresponding to the reduction of β-NiOOH to β-Ni(OH)₂. The current density flowing along the anodic oxidation peak varies with the concentration of the electrolyte according to: where a and b are constants. An increase in the scan rate increases markedly the current density flowing along the whole range of the CVs. As the concentration of borate anions increases, the anodic peak potential is shifted toward more positive values, whereas the cathodic peak potential is shifted in the negative direction, indicating the irreversibility of formation of the passive film formed on the electrode surface. A correlation is made between the anodic oxidation processes and their corresponding cathodic one. The failure-protecting film in borate solutions is assumed to be caused by the formation of a sandwich oxide having the form: NiO/β-Ni(OH)₂/β-NiOOH.     

Petrophysical characterization and durability aspects of tufa rocks at Kurkur Oasis,Western Desert,Egypt

Bulletin of Engineering Geology and the Environment - Various kinds of rocks can be used as building stones based on their durability, appearance, and availability. During many periods of times,...     

Magnetic properties of (Fe1−x M x )7Se8

The temperature dependence of the magnetization of the quenched and slowly cooled samples of Fe₇Se₈ and (Fe_1–x M _x )₇Se₈ samples with M = cobalt and nickel and x=0.02, 0.05 and 0.08 are given. All the thermomagnetic curves obtained belong to the Weiss ferrimagnetic type. Discontinuities indicating a magnetic transformation to antiferromagnetic order were obtained for some samples. The magnetic moment at 0 and 78 K (M ₀ and M₇₈) dependence on nickel and cobalt concentrations are given. The temperature dependence of the reciprocal susceptibility in the paramagnetic range was studied, and the asymptotic Curie points are given. The values of the effective magnetic moment, _eff, and the number of unpaired electrons were calculated. The thermal variation of the electrical conductivity of the host material, Fe₇Se₈, is given.     

Synthesis and characterization of Na‐alginate/acrylamide hydrogel and its application in dye removal

Sodium‐alginate/acrylamide (Na‐alginate/AAm) cross‐linked hydrogel was prepared by using gamma irradiation. The gel content and the water absorbency behavior of the obtained hydrogel were investigated. The thermal and morphological properties of the prepared hydrogel were studied using thermogravimetric analysis and scanning electron microscopy. The thermal stability of Na‐alginate significantly changed when mixed with AAm. The adsorption of basic violet 7 dye on the prepared hydrogel was studied under different experimental conditions. The adsorption process for the basic dye was proven pH dependent. The maximum amount adsorbed (mg/g) of the Na‐alginate/AAm for the dye was found to be 78.1.0 mg/g at pH 9.0. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011